An imaging element having a general linear photoelectric conversion characteristic cannot accurately acquire a luminance distribution on a dark portion or a bright portion even with respect to an ordinary subject due to the narrow dynamic range thereof. Further, although an imaging element with a logarithmic conversion type photoelectric conversion characteristic has a sufficiently wide dynamic range with respect to an ordinary subject, the imaging element may have a poor sensitivity on the low luminance side.
In view of the above, for instance, as disclosed in patent literature 1, there has been known a linear-logarithmic conversion type imaging element (hereinafter, called as a “linear-log sensor”) having two photoelectric conversion characteristics (hereinafter, called as “a linear-log characteristic”) i.e. a linear characteristic and a logarithmic characteristic in accordance with an incident light amount. Such a linear-log sensor is capable of satisfying both of the requirements on sensitivity and wide dynamic range by performing an imaging operation with a linear characteristic having a high sensitivity on the low luminance side, and by performing an imaging operation with a logarithmic characteristic having a wide dynamic range on the high luminance side.
Further, for instance, as disclosed in patent literature 2, there has been known a method for acquiring an image having a wide dynamic range by combining images obtained by performing imaging operations while changing an exposure time, with use of an imaging element having a linear photoelectric conversion characteristic. In addition to the above, there has been proposed a sensor having a so-called knee characteristic i.e. a linear photoelectric conversion characteristic having gradients different from each other in accordance with an incident light amount.
On the other hand, for instance, as disclosed in non-patent literature 1, there has been developed a so-called night view function. To perform the night view function, a near infrared camera is loaded in an automobile to display images of pedestrians and/or vehicles in a front direction at nighttime on a monitor. However, an image obtained by the near infrared camera is monochromatic and is different from an image directly viewed by human eyes. This may provide the viewers incongruity.
Further, there has also been known an imaging apparatus for imaging a night scene in colors. For instance, patent literature 3 discloses an imaging apparatus for generating a pseudo color image by extracting visible image data composed of R, G, and B color components, and infrared image data, with use of image data obtained by an imaging element provided with R, G, and B color filters, and an Ir filter for transmitting infrared light; and by generating luminance information by applying a weight to luminance information obtained from the visible image data and luminance information obtained from the infrared image data.
However, since the quantity of photon is small at nighttime, the S/N ratio of an image obtained at nighttime may be small. Patent literature 3, however, does not consider such a drawback.
Further, non-patent literature 1 involves a drawback that an image may be less visible, because the viewer may be blinded by strong light such as headlight from an opposing automobile.